Gateway Plaza Wilmington, DE Elizabeth Hostutler Structural Option.

Gateway PlazaWilmington, DE

Elizabeth HostutlerStructural Option

Presentation Outline• Project Overview• Depth Study• Breadth Studies

– Mechanical: duct design

– Construction Management: scheduling and cost estimates.

• Cost Analysis• Conclusions

GATEWAY PLAZAWilmington, DE

Elizabeth Hostutler – Structural Option – Spring 2006

PROJECT INFORMATION



Project Information-Key Players• Buccini/Pollin Group• Gilbane• Gensler• Engineers

– Landmark Engineering– Duffield Assoc., Inc.– BALA Consulting Engineers, Inc.– O’Donnell Naccarato & MacIntosh



Project Information-Overview• Location: 500 Delaware Ave.• 15 stories + mechanical penthouse

(210’-6”)– 1st level: retail space & lobby.– 14 floors office space for tenant fit-out.

• July 2005-December 2006• $52 million (17% structural system)• 387,000 ft2

• 5-story parking garage in rear• Tinted glass curtain wall façade



Project Information: Existing Conditions

• Composite steel framing• Concrete filled steel pile

foundations with pile cap• 6-¼” slab on deck• 30-1/4” floor depth.• Concentrically braced frames.

N



Service Core

STAIRS STAIRSREST-

ROOMSMECH.ROOM

ELEVATORLOBBY

Project Information: Existing Conditions

N



52’-6”x30’-0” and 36’-0”x30’-0” typical bays.

52’-6” x 30’-0” bay

36’-0” x 30’-0” bay

DEPTH STUDY



Depth Study-Post-tensioned Concrete Floor

• Design Objectives:– Preserve long span bays.– Limit floor depth to 24”.

• Feasibility Factors:– Cost– Schedule– Impact on foundations




• Design: One-way post-tensioned concrete slab with post-tensioned beams framing along column lines.

• Criteria:– 6000 psi concrete

– 8” thick slab

– 52.5’ long beams: 24”x 36” beams




Tendon Layout




• Final Design:– Initial jacking force: 1303 k in slab and

1040 k in beams.– (6)-½” dia banded tendons in slab.– Tendons spaced 6’ apart.– 39 tendons in longitude beams.– 20 tendons in latitude beams.




• Initial Service Loading




• Sustained Service Loading



Depth Study-Lateral System



• Problems:

– Increased weight impacted seismic.

– Eccentricity created torsion.

– Limiting drift to H/600 = 4.21”

• Solutions:

– Added 1 shearwall between mechanical room and elevator lobby.

– Considered concrete frames to resist lateral load.

– Maximum drift was 3” (H/840).

Depth Study-Lateral System• Shearwalls: 12” thick 4000 psi with #6 @ 14” o.c.

N



Additional shearwall

Depth Study-Lateral System



Seismic Loads in east-west direction: 0.9D + 1.0 E

Wind Loads in north-south direction: 1.2D + 1.6W + L + 0.5

Lr

Depth Study-Impact on Foundation• Increase foundation loads by an

average 38%.• Change foundations to end-

bearing caissons.– Minimum size: 3.5’ diameter– Maximum Size: 6.5’ diameter

Concrete Steel

B 2 1107 k 307 k1 1151 k 754 k

C 3.7 98 k 98 k3 957 k 829 k2 2434 k 1796 k1 1597 k 1325 k

K 3.7 98 k 81 k3 992 k 831 k2 2069 k 1490 k1.4 1203 k 943 k

Location



BREADTH STUDIES



MECHANICAL STUDY



Mechanical Study

• Check for proper indoor air quality.• Design ductwork.



Mechanical Study• Existing system:

– Rooftop cooling tower.

– Heat pump and air conditioning unit in each mechanical room.

– 26”x96” main supply duct on each floor.

• 24”x24” supply and return diffusers.

• Ceiling plenum return.



Mechanical Study



Typical open office floor plan for 6 tenants.

Mechanical Study



• Supply diffuser layout with 16’ air throws.

• 650 cfm per diffuser.

Mechanical Study• Supply ducts with return stub ducts.

– Largest: 68”x20”

– Smallest: 10”x10”

Exhaust LouverReturn grill



CONSTRUCTION MANAGEMENT

STUDY



Construction Management Study• Schedule Comparison• Cost Comparison• Rough estimate of foundation costs and

comparison.



Construction Management Study-Scheduling• Duration: 156 days

– Columns (F/R/P): 2 days• Forming• Tying Reinforcement• Pouring and curing

– Construct/Erect shoring and formwork: 3 days

– Tie reinforcement for slab and beams: 1 day

– Rough-in for MEP: 1 day– Concrete (for each section):

• Pour and finish: 1 day• Cure: 2 days

– Strip formwork & reshore: 2 days– Jack the post-tensioning tendons: 1

day

0

20

40

60

80

100

120

140

160

Duration

Concrete

Steel



Construction Management Study-Estimates

Amount Material Labor Equipment Cost

03110-405 Beam formwork 7044 SFCA 0.91 4.05 $63,46603110-420 slab edge forms 479 SFCA 0.48 4.6 $2,432

slab formwork 21910 sf 1.3 2.86 $216,47103210-600 Slab Reinforcing 46.18 tons 800 380 $72,041032230-600 Ungrouted Post-tensioned strand 26350 lb 0.47 0.87 0.02 $58,76103300-220 6000 psi Concrete 687 CY 109 $74,88303310-700 Placing 687 CY 11.5 4.7 $11,129

Total $499,183

03310-240 24"x24" average reinforcing including 4 use forms, concrete, placement, reinforcing

72 CY 370 400 41 $58,392

Total $58,392

B2010-101 12" thick, plain finish, 4000 psi wall including 4 use forms, reinforcing, concrete, placement

3402 sf 6.6 15.35 21.95 $97,127

Total $97,127

Total $654,702Cost/sf $28

Estimate of Post-tensioned Concrete Design for One Typical FloorSlabs System

Columns

Shearwalls




Amount Material Labor Equipment Total Cost05310-300 20 ga. 3-1/4" Metal Deck 23403 SF 1.88 0.34 0.02 $60,38003210-200 6x6 W1.4xW1.4 234 CSF 19.35 17.35 $12,64903300-220 6000 psi concrete 253 CY 81 $20,47803310-700 Placing concrete 253 CY 13.1 5.35 $4,66405120-260 Curb Edging 718 LF 14 4.95 0.33 $17,397

Total $98,171

05120-680 Offices over 15-stories 107 TON 1900 345 109 $251,87805090-840 3/4" dia Shear Studs 27352 0.49 0.67 0.28 $57,713

Total $309,591

05120-680Columns, Beams, and Braces 50 TON 1900 345 109 $117,700

07800-600 Decking 22000 SF 0.62 0.54 0.09 $51,260Beams 17295 SF 0.41 0.45 0.07 $31,650Columns 3506 SF 0.47 0.62 0.1 $8,521Total $91,430

TOTAL $616,892Cost/sf $26

Frames

Fireproofing

Estimate of Composite Steel Design for One Typical Floor

Slabs System

Structural Steel




Amount Material Labor Equipment Cost

A1020-310 4'-0" dia. x 100' 20 Ea 4358 70459 $1,496,3295'-0" dia. x 100' 6 Ea 8064 144990 $918,3246'-0" dia. x 100' 10 Ea 11730 172277 $1,840,069

TOTAL $4,254,722

A1020-130 End Bearing Steel Piles Amount Material Labor Equipment Cost2380 4 pile cluster 5 5625 3325 $44,7502460 6 pile cluster 8 8425 5025 $107,6002480 7 pile cluster 7 9825 5850 $109,7252500 8 pile cluster 5 12600 7525 $100,6252560 12 pile cluster 9 15400 9200 $221,400

03310-240 Pile caps, incl. forms and reinf. 612 108 49 0.31 $96,309TOTAL $680,409

Caissons

Concrete Filled, Drilled Piers



Construction Management Study

Total Cost Cost/Floor Cost/sf Duration Foundations

Concrete $ 10,475,227 $ 654,702 $27.98 156 $4,254,722Steel $ 9,870,274 $ 616,892 $ 26.36 140 $680,409

System Comparison



CONCLUSIONS



Conclusions• Post-tensioned system is viable based on cost and

schedule, not on foundations.• Achieved savings of 6.25”/floor=100” total.



AcknowledgementsO’Donnell Naccarato & MacIntosh

Peter Paton, Structural Engineer

GilbaneCraig Hedlund, Construction Manager

Dr. Linda Hanagan

RAM Concept Technical Support

Chad Illig Anthony Lucositic

David J. MelfiJustin MulhollanSteven Puchek



QUESTIONS?



Gateway Plaza Wilmington, DE Elizabeth Hostutler Structural Option.

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